Electrode for resistance furnace

ABSTRACT

An electrode for a resistance analytical furnace has a central opening including a crucible-engaging surface and an annular flange spaced from the crucible-engaging surface. The flange has a lower surface with a plurality of grooves formed therein. The grooves are curved and extend from the central opening of the edge of the flange.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/358,096 entitled VACUUM CLEANING STRUCTURE FOR ELECTRODE FURNACE,filed on Jan. 25, 2012, by Octavio R. Latino, et al., which claimedpriority under 35 U.S.C. §119(e) and the benefit of U.S. ProvisionalApplication No. 61/444,294, entitled VACUUM CLEANING INTERFACE FORELECTRODE FURNACE, filed on Feb. 18, 2011, by Octavio R. Latino, et al.,the entire disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to analytical furnaces and particularly toan improved electrode and vacuum system for cleaning the electrodes andfurnace area of a resistance furnace.

Analytical furnaces heat specimens, such as chips and pin samples, andthe like, typically ranging in mass of about 1 gram or less in acrucible. Resistance furnaces employ graphite crucibles clamped betweentwo electrodes which pass an electrical current through the crucible,heating specimens to temperatures of 2500° C. or higher. The gaseousbyproducts of fusing the specimen are then swept by an inert gas throughthe furnace system to an analyzer for the subsequent analysis of thespecimen gases of interest using suitable detectors. Such an analyzer isrepresented by Model TCH600 commercially available from Leco Corporationof St. Joseph, Mich.

During the heating of a specimen, the enclosed furnace chamber becomescontaminated with debris, dust, soot, and the like from the byproductsof fusing the sample and needs to be frequently cleaned. In the past,between cycles of analysis, a vacuum was supplied to the general area ofthe electrodes for removing such dust and debris. Also, a powered rotarybrush has been employed in the furnace area of a resistance furnace toremove debris from the electrodes. Although such a system has beenrelatively successful, with the increased sensitivity of detectors andthe ability to measure lower levels of analytes, there remains a need tomore frequently clean the furnace as well as improve the cleaning ofanalytical furnaces between analyses.

SUMMARY Of THE INVENTION

The system of this invention provides an improved electrode andelectrode cleaning manifold which is positioned on the electrode toincrease the airflow turbulence for removal of dust and debris duringcleaning of an analytical furnace. One embodiment of the invention is anelectrode for engaging a crucible, which electrode has an end spacedfrom the crucible-engaging surface with a plurality of grooves formedtherein, allowing cleaning air to flow through the grooves. In anotherembodiment, a manifold for fitting over the end of the electrode isprovided to provide a dust recovery plenum. An outlet communicating withthe plenum is coupled to a vacuum source to remove debris from thefurnace and electrode. Systems embodying the present invention includean electrode having an end with a plurality of curved grooves formedtherein and a manifold, which fits over the end of the electrode. Themanifold defines a dust recovery plenum coupled to an outlet forcoupling to a vacuum source to remove debris from the furnace andelectrode. In a further embodiment, the system also includes an abradingbrush used concurrently with the dust removing vacuum source.

With these improvements, the analytical furnace can be frequentlycleaned and the quality of cleaning improved. These and other features,objects and advantages of the present invention will become apparentupon reading the following description thereof together with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is front perspective view of an analyzer including a fusionfurnace having the improved electrode cleaning system of the presentinvention;

FIG. 2 is a fragmentary cross-sectional view of the furnace for aninstrument as shown in FIG. 1, showing a crucible in place during afusion cycle;

FIG. 3 is a bottom perspective cut-away view, partly in phantom, of theupper furnace electrode and cleaning manifold attached thereto;

FIG. 4 is a bottom plan view of the upper electrode and manifold partlyshown in phantom;

FIG. 5 is a vertical cross-sectional view of the upper electrode,manifold, and lower electrode in an open position with the electrodebrush cleaner in a use position;

FIG. 6 is a vertical cross-sectional view of the upper electrode andlower electrode engaged for fusing a specimen in a crucible and showingthe carrier gas flow path;

FIG. 7 is a vertical cross-sectional view of the structure shown in FIG.6, showing the lower electrode being lowered and separated from theupper electrode during initiation of a cleaning cycle and showing thecleaning airflow path;

FIG. 8 is a bottom plan view of the end of the upper electrode;

FIG. 9 is a perspective view of the upper electrode;

FIG. 10 is a bottom perspective view of the manifold which is mounted tothe upper electrode;

FIG. 11 is a top perspective view of the manifold;

FIG. 12 is a perspective view of the upper electrode coupled to themanifold;

FIG. 13 is a vertical cross-sectional view of the furnace and a cleaningbrush mechanism shown partially raised into the furnace and showing thecleaning airflow path; and

FIG. 14 is a cross-sectional view of the furnace shown with the cleaningbrush fully engaged with the upper electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, there is shown an analytical instrument10, such as a Model ONH836 nitrogen, oxygen, hydrogen analyzer,commercially available from Leco Corporation of St. Joseph, Mich. Theinstrument is designed to incorporate the present invention and includesa resistance furnace 16, as best seen in FIG. 2. The furnace includes anupper electrode 20 incorporating one aspect of the present invention anda lower electrode 30 which sealably encloses the furnace chamber withinthe upper electrode and engages a graphite crucible 40 positionedbetween the upper and lower electrodes. A suitable power supply isconventionally coupled to the upper and lower electrodes to passsufficient current through crucible 40 to heat a sample specimencontained therein to a temperature of 2500° C. or higher to releaseanalyte gases from the sample. As is well known, a supply of inertcarrier gas, such as helium, flows downwardly through the centralopening 22 of upper electrode 20 in the direction indicated by the flowpath identified by arrow A into the mouth of the crucible and exits thechamber through a gas outlet port 52 in electrode 20. Port 52 is acylindrical tube which extends through manifold 50 embodying one aspectof the present invention and supplies the flow of inert gas and analytein a conventional flow path to the analyzer 13 (FIG. 1) for analysis.

The lower electrode 30 is raised and lowered in a conventional manner bya movable pedestal 32 coupled to an actuating cylinder (not shown) whichraises it into a position for heating of the sample, as shown in FIG. 2,and lowers the lower electrode 30, as shown in FIG. 5, to allow anautomatic cleaning brush assembly 12 (FIGS. 1, 5, 13, and 14) to moveinto position for brushing the interior of the furnace 16, includingsurfaces of members 22 and 29 of the upper electrode as an optionalcleaning step. With the improved cleaning airflow provided by the upperelectrode design and manifold, some cleaning cycles can eliminate thebrushing step provided by assembly 12 and use only the vacuum cleaning,thus, greatly reducing the time between successive analyses. Typically,however, the upper electrode is also cleaned by the rotary brush 70(FIG. 14) with the loose debris being removed through vacuum line 14coupled to vacuum manifold outlet 54. The unique design of electrode 20and manifold 50 provides a highly improved flow rate and turbulence ofair through the furnace 16 to sweep the loosened debris from thefurnace. Before describing the interrelationship of the upper electrode20 and manifold 50 to achieve this aspect of the invention, adescription of each of these elements is presented.

Referring initially to the upper electrode construction shown in FIGS.2-4, 6, and 9, the upper electrode 20 has a generally cylindrical body24 with grooves 25 formed therein for cooling when sealed in coolingchamber 11 (FIGS. 2 and 3) by upper and lower O-rings 15. The upperelectrode includes a central, generally cylindrical passageway 22 forreceiving a sample from a sample drop assembly 65, which can be of thetype disclosed in U.S. Pat. No. 6,291,802, entitled SAMPLE INTRODUCTIONASSEMBLY, the disclosure of which is incorporated herein by reference.Passageway 22 is generally cylindrical and extends along the axis of thecylindrical body 24 for the passage of an inert carrier gas,, such ashelium, as seen by arrow A in FIG. 2. The lower end of the cylindricalpassageway 22 enlarges in diameter to define the cylindricalcrucible-receiving furnace 16. Electrode 20 includes a lower flange 26with apertures 21 (FIGS. 4 and 8) for mounting the electrode to thecooling chamber 11 of the furnace 16 utilizing conventional fasteners 17(FIG. 3). Flange 26 also includes apertures 23 for securing manifold 50to the flange 26, as shown in FIGS. 3, 6, 7, and 12, using conventionalfasteners 19 (FIG. 3). Gas outlet port 52 extends through a slot 51(FIGS. 11 and 12) in manifold 50 and communicates with the furnace 16and passageway 22 in upper electrode 20 for allowing the analyte andcarrier gas to exit through the port 52, as shown by arrow A in FIG. 2,and into the analyzer instrument 13 (FIG. 1).

Flange 26 includes a lower surface 27 (FIGS. 4 and 8) into which aplurality of angularly spaced-apart (about 40°) curved helical grooves28 are formed. In the embodiment shown, eight grooves numbered 1-8 (FIG.8) are employed. Grooves 28 spiral radially outwardly and, together withmanifold 50, provide a turbulent airflow path, as illustrated by arrow Bin FIGS. 7, 13, and 14, for removing debris from the furnace 16 (FIGS. 6and 7) defined, in part, by the interior space of the enlarged lowerarea of passageway 22 of upper electrode 20. The grooves 28progressively increase in depth from their inner radius to the outerradius of flange 26 with the dimensions of one embodiment beingillustrated in Table 1. These dimensions may be varied ±20% fordifferent furnace designs. This helical design of the eight grooves 28provides a turbulent airflow when the vacuum hose 14 is coupled tofitting 54 and the furnace is opened, as seen in FIGS. 5, 13, and 14,for the efficient removal of debris from the electrode area.

TABLE 1 GROOVE # START DEPTH END DEPTH FIG. 8: 1 .100 inch .100 inch 2.100 inch .125 inch 3 .100 inch .150 inch 4 .100 inch .175 inch 5 .100inch .200 inch 6 .100 inch .225 inch 7 .100 inch .250 inch 8 .100 inch.275 inch

The upper copper electrode includes a crucible-engaging contact, whichis an annular tungsten-copper alloy insert 29 (FIGS. 2, 6, and 7) toprovide wear resistance and durability for the electrode. Insert 29contacts the upper annular surface of crucible 40, as illustrated inthese figures. The lower electrode 30 is of conventional design employedin the past for the TCH600, including a tungsten-copper alloy crucibleholder 36 (FIG. 6).

The manifold 50, which is mounted to the upper electrode 20, can beintegrally molded of a suitable polymeric material, such as polyetherether ketone (PEEK), and includes a vacuum outlet fitting 54 which iscoupled to a vacuum source, such as vacuum hose 14 (FIG. 1), which, inturn, is coupled to a commercial canister-type vacuum cleaner (notshown) for providing sufficient airflow rate to withdraw dust and debrisfrom the electrode area. Manifold 50, as best seen in FIGS. 10 and 11,has a generally annular floor 56 with apertures 55 aligned withapertures 23 in lower electrode flange 26. The inner surface of floor 56(FIG. 11) is immediately adjacent and in contact with the outer surface27 of flange 26 of upper electrode 20, as generally illustrated in theassembled view of FIGS. 7 and 12. The circular opening 57 in manifold 50provides access for the lower electrode 30 to raise and lower a crucible40 into and out of the furnace 16 of the upper electrode 20, as seen inFIGS. 6 and 7.

Vacuum outlet 54 communicates with and extends in tangentialrelationship to the annular plenum 60 (FIGS. 6 and 7) defined by theinner surface of the generally circular outer wall 58 of manifold 50 toimprove the efficiency of the airflow drawn by the vacuum hose 14through the furnace 16 during cleaning. The outer wall 58 of themanifold 50 terminates at its upper end in an inwardly extending lip 59,which extends in closely spaced relationship to the outer surface 31 offlange 26 of upper electrode 20, as illustrated in FIGS. 6 and 7. Theannular space between the inner surface of generally circular wall 58and between floor 56 and lip 59 defines an annular plenum 60 (FIGS. 3,4, 6, and 7), which is generally rectangular and surrounds the flange 26and communicates with grooves 28 in electrode 20. Plenum 60 communicatesdirectly with the vacuum outlet 54. The manifold 50 includes a sealedoff slot 51 through side wall 58 to allow the gas outlet port 52 fromupper electrode 20 to extend therethrough, as seen in FIG. 12.

FIGS. 6 and 7 illustrate the flow paths of carrier gas and analyteduring heating of a sample (arrow A) as well as during the vacuumcleaning cycle (arrow B), respectively. In FIG. 6, the lower electrode30 is raised into a position in which its O-ring 34 seals the furnace 16defined by the inner cylindrical walls of passageway 22 of upperelectrode 20. In this position, the crucible 40 receives a supply ofelectrical current heating the crucible to indirectly heat a specimen.An inert carrier gas flows in the direction indicated by arrow A andremoves the gaseous byproducts from a fused sample contained in thecrucible 40 through the gas outlet port 52 formed in the electrode andextending through the slot 51 in manifold 50. In the position shown inFIG. 6, there exists a slight gap between the lower outer annularsurface of floor 56 of manifold 50 and the upper annular surface 38 oflower electrode 30, allowing an airflow path, as shown by arrow B,between the larger diameter of opening 57 in the floor 56 and thesmaller outer diameter of lower electrode in area 37 (FIG. 6). Thisallows air to flow into plenum 60 through grooves 28. This provides anairflow path through the vacuum outlet 54 when vacuum is applied to thehose 14 during heating of a sample.

After fusion of the sample and analysis of the sample gas, the lowerelectrode is withdrawn, as illustrated in FIG. 7, lowering in adirection indicated by arrow C, and air is admitted through the top ofthe upper electrode and passageway 22, as indicated by arrow B in FIG.12, to provide an abundance of airflow through the furnace 16surrounding crucible 40. The air admitted through passageway 22 ofelectrode 20 is provided by opening the sealed slide block inconjunction with the gate valve in the sample drop assembly 65 (FIGS. 13and 14) exposing passageway 22 to the atmosphere. Thus, as the lowerelectrode is initially moved from a totally sealed position (shown inFIG. 6) to a partially sealed position (shown in FIG. 7), a relativelyhigh velocity spiral flow of air passes through the furnace 16 andgrooves 28 in the upper electrode and into plenum 60. This flow exhauststhrough the vacuum outlet 54 removing dust and debris from the furnaceand areas between the upper and lower electrodes.

In some models of the analyzer, a cleaning brush assembly 12 (FIG. 1) isemployed and swings into position and is activated, as shown in FIGS. 13and 14, to raise a stepped rotary brush 70 and abrader 71 into thefurnace 16, as illustrated in FIG. 14, to mechanically abrade the innersurfaces of electrode 20 and insert 29 for removal of debris.

It will become apparent to those skilled in the art that variousmodifications to the preferred embodiment of the invention as describedherein can be made without departing from the spirit or scope of theinvention as defined by the appended claims.

The invention claimed is:
 1. An electrode for an analytical resistancefurnace comprising: a generally cylindrical electrode having a centralopening for receiving a crucible, said electrode having acrucible-engaging contact and an end spaced from said crucible-engagingcontact having a plurality of grooves formed therein.
 2. The electrodeas defined in claim 1 wherein said grooves are curved.
 3. The electrodeas defined in claim 2 wherein said grooves are helical.
 4. The electrodeas defined in claim 3 wherein said grooves increase in size in aradially outward direction.
 5. The electrode as defined in claim 4wherein said grooves extend tangentially to an outer cylindrical surfaceof said electrode.
 6. The electrode as defined in claim 1 wherein saidelectrode includes a generally cylindrical body and said end spaced fromsaid crucible-engaging contact is an enlarged diameter annular flangehaving a lower surface.
 7. The electrode as defined in claim 6 whereinsaid grooves are formed in said lower surface of said annular flange. 8.The electrode as defined in claim 7 wherein said body includes aplurality of cooling grooves formed in an outer surface of said body. 9.The electrode as defined in claim 1 wherein said grooves are helical andincrease in depth in a radially outward direction from said centralopening from about 0.1 inches to about 0.275 inches.
 10. The electrodeas defined in claim 1 wherein said electrode is made of a conductivematerial and wherein said crucible-engaging contact includes atungsten-copper insert.
 11. An electrode for an analytical resistancefurnace comprising: a generally cylindrical electrode body having acentral axially extending cylindrical opening having an enlarged lowerend for receiving a crucible, said electrode having an annular flange atsaid lower end, said flange having a diameter greater than the diameterof said body and having a lower surface; and a plurality of radiallyoutwardly extending grooves formed in said lower surface of said flange.12. The electrode as defined in claim 11 wherein said grooves arecurved.
 13. The electrode as defined in claim 11 wherein said groovesare helical.
 14. The electrode as defined in claim 11 wherein saidgrooves increase in size in a radially outward direction.
 15. Theelectrode as defined in claim 11 wherein said grooves extendtangentially from said cylindrical opening to an outer edge of saidannular flange.
 16. The electrode as defined in claim 11 and furtherincluding a crucible-engaging contact in said enlarged lower end andspaced from said annular flange.
 17. The electrode as defined in claim16 wherein said crucible-engaging contact is made of tungsten carbide.18. An electrode for an analytical resistance furnace comprising: agenerally cylindrical electrode body having a central axially extendingcylindrical opening having an enlarged lower end for receiving acrucible; an annular flange at a lower end of said electrode, saidflange having a diameter greater than the diameter of said body andhaving a lower surface; and a plurality of radially outwardly extendingcurved grooves formed in said lower surface of said flange and extendingfrom said cylindrical to an outer edge of said flange.
 19. The electrodeas defined in claim 18 wherein said grooves are helical.
 20. Theelectrode as defined in claim 18 wherein said grooves increase in sizein a radially outward direction.